Note 33 — Chapter IX · COMPOUNDS OF CARBON WITH OXYGEN AND NITROGEN

Thus, for instance, oxamide, or the amide of oxalic acid, (CNH2O)2, is obtained in the form of an insoluble precipitate on adding a solution of ammonia to an alcoholic solution of ethyl oxalate, (CO2C2H5)2, which is formed by the action of oxalic acid on alcohol: (CHO2)2 + 2(C2H5)OH = 2HOH + (CO2C2H5)2. As the nearest derivatives of ammonia, the amides treated with alkalis yield ammonia and form the salt of the acid. The nitriles do not, however, give similar reactions so readily. The majority of amides corresponding to acids have a composition RNH2, and therefore recombine with water with great ease even when simply boiled with it, and with still greater facility in presence of acids or alkalis. Under the action of alkalis the amides naturally give off ammonia, through the combination of water with the amide, when a salt of the acid from which the amide was derived is formed: RNH2 + KHO = RKO + NH3.

The same reaction takes place with acids, only an ammoniacal salt of the acid is of course formed whilst the acid held in the amide is liberated: RNH₂ + HCl + H₂O = RHO + NH₄Cl.

Thus in the majority of cases amides easily pass into ammoniacal salts, but they differ essentially from them. No ammoniacal salt sublimes or volatilises unchanged, and generally when heated it gives off water and yields an amide, whilst many amides volatilise without alteration and frequently are volatile crystalline substances which may be easily sublimed. Such, for instance, are the amides of benzoic, formic, and many other organic acids.